The invention relates to a method for focusing the shooting lens of a motion picture or video camera and to a device for carrying out the method.
In order to adjust the image sharpness or to focus shooting images or shooting sequences, which are shot by a motion picture camera via a shooting lens, it is known to connect a sharpness setting instrument, which is operated manually by an image sharpness or camera assistant in order to unburden the cameraman, to the shooting lens. Either the sharpness setting instrument is connected mechanically to the lens ring for image sharpness adjustment of the shooting lens, or an electric motor-driven drive unit arranged in a horizontal or vertical arrangement on the shooting lens transmits a torque via a toothed pinion onto the outer teeth of the image sharpness lens ring for sharpness adjustment according to EP 0 575 022 B1.
At the same time, in EP 0 942 305 A1 a device coupled to the lens ring for determining the actual status of the lens ring position, which determines the real position of the lens ring relative to the lens and converts this into a measurement output signal, may be provided in conjunction with the drive unit for adjusting the position of the image sharpness lens ring.
According to EP 0 574 105 A1, the drive unit for image sharpness adjustment may be driven via a control system which comprises a plurality of motor units coupled to the lens rings of the shooting lens of a motion picture camera according to EP 0 575 022 B1 for zoom, focus and iris adjustment, into which position transducers are integrated, and one or more hand operating units with which both adjustment values and distance limits can be adjusted in analogue and/or electronic fashion. The motor units and the hand operating unit are connected together via a serial control and data bus.
As an alternative according to DE 196 29 484 A1, a connection may be established between the drive units and position transducers, coupled to the lens rings of the shooting lens of the motion picture camera, with one or more hand operating units for zoom, image sharpness and iris adjustment via wireless control and monitoring of camera functions and therefore for image sharpness adjustment, in which a camera-side control and acquisition unit is connected via line connections to the focus, zoom and iris drive unit and contains a radio modem, which transmits control signals to and receives them from a remote operating control unit. The user-side control unit comprises a hand wheel for focusing or image sharpness adjustment, which is backed by a scale on which the range limits for image sharpness adjustment can be set. A potentiometer connected to the hand wheel specifies absolute values as setpoint values for adjusting the image sharpness on the shooting lens, which are transmitted via the radio transmission link to the camera-side control and acquisition unit that adjusts the motor or drive unit connected to the image sharpness lens rings to the setpoint position specified by the user-side control unit for adjusting the image sharpness lens rings.
In the methods and devices cited above, the focusing or distance setting of the shooting lens is carried out manually by specifying a corresponding distance setpoint value, which is either measured by means of a tape measure or estimated for example with the aid of marking points surveyed before shooting.
Since manual focusing of a shooting lens is susceptible to error and can be carried out only with difficulty in special shooting situations, for example with very long or very short distances and with very fast image sharpness changes, DE 42 05 397 A1 discloses automatic focusing of a shooting lens in which an autofocus instrument acquires the distance between a shooting object and the motion picture camera by means of an ultrasound or laser rangefinder and sets the image sharpness, required for focusing the shooting image or shooting sequence, on the shooting lens of the motion picture camera.
Since the entire image content does not always lie at the focus when shooting a subject or a scene, the problem of aligning the distance measurement instrument at the object to be focused inside a shooting image arises in automatic focusing instruments.